What does "Prevailing Visibility" refer to?

"Prevailing Visibility" refers to the visibility that is most common in a given area, typically being the maximum visibility observed in sectors comprising half or more of the horizon circle. This measurement is crucial for pilots and meteorologists because it factors into flight safety and operations. It is an important indicator for assessing conditions that may affect aircraft operations, particularly during takeoff, landing, and navigation.

For example, if visibility is significantly better in certain directions while being poorer in others, it is the broader and more reliable measure—the prevailing visibility—that gives a pilot the best understanding of what to expect on approach or during flight. Thus, the emphasis on sectors that constitute a majority of the horizon ensures that safety measures are based on the most representative visual conditions available.